This invention relates to a device for correctly positioning the yarns prior to knitting in a circular knitting machine, in particular a hose knitting machine.
More specifically, reference will be made hereinafter to a double cylinder circular hose knitting machine, without the invention being limited to just that application.
It is known that, for correctly positioning a yarn to be knitted in a double cylinder circular knitting machine, a pneumatic device is currently employed which comprises suitably oriented blowing nozzles operative to bring the yarn close to the needles and release the yarn from the gripping device which holds it while it is not being knitted by the needles.
The basic problem is that of ensuring that the yarn is picked up by the needles, which cannot be made quite certain by the mere mechanical approach of the yarn feeding finger to the needle path, and that of ensuring that the yarn is released from the gripping device such that it can run freely as it is being set to knit by the needles.
It is further necessary that the blowing devices cut in timely and synchronically with the actuation of the other members involved, that is the cutting in of the yarn feeding finger and releasing of the gripping device. For this purpose, cams associated with the yarn feeding finger control unit are provided, which cams actuate, through a number of intervening members, valves adapted for admitting pressurized fluid to the blowing nozzles. However, that construction takes up much space, so that its application is limited to but one of the striper units included in the machine, that is to a single feed. For the remaining striper units, i.e. the remaining feeds, the blowing device is put under control by the machine main chain. However, this implies an imperfectly synchronized action with the respective yarn feeding fingers, because the control impulse, as derived from the main chain, can only be applied as the chain is moving forward and must be maintained throughout the time that the chain is held stationary prior to the successive moving step.
It will be appreciated, moreover, that the space requirements of such a system are aggravated by the necessary presence of members for picking up the control impulse from the chain and transferring it to the blowing devices. If a higher number of yarn feeds is used, then a correspondingly higher number of main chain operated controls must also be provided, which conrols, among others, would have to cut in at successive times, owing to the feeds being angularly offset about the needle cylinder; but a control impulse derived from the main chain, which is advanced stepwise, would not allow such a cutting-in in succession.